The present invention relates to a cooling mechanism and method used in a garment such as a suit or vest, as well in a head covering. More particularly, the present invention is directed to cooling devices such as vests, pads or patches used as a new cooling method in, for example, space suits, moisture-tight sealed hazardous material suits, vests and the like in which interior temperature and perspiration increases with physical exertion such as may be encountered in outer space extra vehicular activities, mining operations, fire departments and hazardous material disposal, or in adsorption-type hazardous material suits that are loose fitting.
U.S. Pat. No. 4,856,294, shows a lightweight cooling vest which uses phase change materials to keep the wearer relatively cool under relatively heavy workload conditions for several hours. The materials act as a thermal diode which draws heat away from the surface of the skin but which also provides an insulating barrier to prevent unwanted cooling of the skin should the skin temperature drop below the phase transition temperature of the material.
Although the cooling vest is quite adequate for use in a vest or similar type of garment, the use of phase-change materials does not provide a sufficient cooling effect in connection with garments used in hostile environments such as may be encountered, for example, with hazardous material suits which must be sealed and therefore moisture-tight or adsorption-type hazardous material suits that are loose fitting but that cannot be opened or removed in a hostile environment. By way of illustration, the phase-change material is capable of handling 200-300 kJ per kilogram of material. Although this is acceptable with open garments such as vests, it is not sufficient with respect to sealed garments such as hazardous materials disposal suits OR SPACE SUITS and the like where moisture cannot escape and there is a significant heat build-up.
Therefore, an object of the present invention is to provide a relatively lightweight cooling mechanism and method for use with sealed garments, but not limited to use to use with sealed garments, which will provide an adequate cooling effect for a person wearing such a garment and engaging physical exertion which produces substantial amounts of perspiration.
The foregoing object has been achieved in accordance with the present invention by utilizing the transport of water vapor from the skin or in a closed system to a desiccant bed which adsorbs the water and produces exothermic heat toward the outside of the suit.
In particular, AN EMBODIMENT OF the present invention utilizes a cooling pad which is attached to a desiccant bed for adsorbing evaporated water from the person wearing the suit. The desiccant is located immediately adjacent to the outer surface of the garment and an open cell thermal insulation layer adjacent an opposite surface of the desiccant material to provide a barrier for resistance to heat flow from the exothermic adsorption process from the desiccant back toward the person's skin. This open cell foam between the person's skin and the thermal insulator permits the passive transfer of water vapor from the skin to the desiccant material where it is adsorbed and, when appropriate, itself to act as a thermal insulation barrier to prevent a backwards heat transfer.
As is well known, evaporation of water vapor from a person's skin requires a latent heat of vaporization which provides an overall cooling effect for the person's body. A thermal insulation layer can comprise, for example, a fine mesh nylon open-cell foam polyurethane foam composite so as to decrease by a large factor the heat flow from the absorption layer back to the wearer's skin where heat is created from the exothermic adsorption process. The desiccant bed can be formed, for example, by heat sealing the desiccant material in a plastic bag, which can be opened to initiate the adsorption process, attached by adhesive or the like to the inside of the hazardous materials handling suit. The bag can be then be discarded after use for the intended period, say six hours, or regenerated.
An advantage of the aforementioned embodiment of the present invention is that the cooling mechanism moves the water as vapor through the open cell foam and allows moisture to pass therethrough to the desiccant bed. As previously noted, the open cell foam can act as a thermal insulator depending on the material chosen; or the pad can have a separate material such as a product sold under the trademark "THINSULATE" by the 3M Company, between the open cell foam and the desiccant bed.
Another advantage and feature of the present invention is that the process of evaporation is substantially endothermic so that an adequate cooling capacity may be achieved within practical weight limitations.
Yet another feature of the present invention is that good thermal insulation is provided next to the skin of the person wearing the garment whereas relatively poor thermal insulation is provided at the outside of the suit so that, although the suit is moisture tight, the heat differential existing between the inside of the desiccant bed and the outside of the suit is high enough to cause the heat to flow in only one direction, namely toward the outside of the suit.
According to still another feature of the present invention, the cooling device may be provided in the form of a quilted pad, the quilting being provided so that the desiccant material will not settle to the bottom of the pad but be confined to a smaller space within the pad. The surface of the pad intended to be attached to the suit can have a self-adhesive surface so that the interface between the desiccant bed and the suit material provides a relatively good heat transfer surface. Another surface of the pad adjacent the open-cell foam which can be a polyurethane can be a peelable film such as polyethylene which can be peeled away to initiate the cooling process by permitting the transport of water vapor and prior thereto to provide shelf-life for the pad.
According to another aspect of the present invention, the cooling pad or pads can be adhered to the front and back of the suit, i.e., the chest area and the back areas. If the suit also has a head piece, a cooling pad can be placed in the vicinity of the top of the head where a substantial proportion of perspiration will occur in relation to the body area of the person. Alternatively, if the use of other equipment either on the chest or the back of the person wearing the suit precludes putting cooling pads in those areas, the cooling pads can be adhered to the suit at the sides.
To further minimize the weight of the cooling pad, particularly in a small area such as the head, a small commercial fan can be employed to pull water to a single point. The fan can be battery operated by, for example, a 12-volt battery.
A cooling pad of practical weight, i.e., ten pounds or less, can hold 40% of its weight in water which adsorbs 800 KJ of energy per kilogram of desiccant material with the known cooling vest which has a capacity of 200--300 KJ per kilogram of phase-change material.
According to another embodiment of the present invention, the cooling device and method may be embodied in a cloth covered open-cell foam, which is backed with a polymer film, so that moisture can enter the foam from the skin side and then be transferred through the foam to the desiccant bed with a battery operated fan. In this embodiment the desiccant bed is located outside the suit. The moisture in the air is removed by the desiccant and the heat generated by the hydration would be transferred through the desiccant bed case to the outside. The desiccant bed is provided with baffles to improve the heat transfer and moisture removal. The dry air can be cooled either by a finned pipe, or returned untreated to the suit and distributed through the cloth covered open-cell foam. This return air maintains a constant pressure in the suit to prevent outside air from entering. The desiccant in the desiccant bed can be any commercially available desiccant.
Another embodiment of the personal cooling device utilizes only one moving part, namely a spring-actuated pressure regulating valve. Working fluid is evaporated from a sealed vest and captured in an absorbent or adsorbent bed which rejects heat to the environment. Rather than use the wearer's perspiration as the working fluid, a self-contained working fluid is used. Although this system requires the additional mass of this working fluid, the rate of adsorption of the working fluid vapor on the bed is increased because no other gases are present in the system to impede this adsorption. Also, this embodiment has the option of using fluids other than water as the working fluid.
In yet another embodiment of the present invention, working fluid is desorbed from an adsorption bed, thereby providing the cooling and capture of this working fluid in an external heat exchanger, such as a condenser, which rejects heat to the environment. For space applications, the working fluid can be exhausted to the vacuum of space instead of being captured. This approach is ideal for a space suit cooling system where the working fluid would be desorbed from the adsorption bed to provide the cooling and the desorbed vapor is dumped to the surrounding space environment. The adsorbent bed could be configured to be a vest, or it could be an intermediate heat exchanger between the cooling system and the wearer. This approach is different from the above-described sealed vest with pressure regulating valve in which the vest is the evaporator and the vapor is driven off the evaporator and trapped in the adsorbent bed where heat is rejected. The desorption embodiment uses a recharging scheme similar to the sealed vest embodiment since in the recharge mode thereof, the bed is heated (adsorbing energy) and drives the working fluid off the bed (adsorbing energy or cooling in the process) and back into the vests which acts as a condenser.